j/^ Conductivity of Aqueous Solutions. Part XI. 



acid and to confirm the experimental accuracy of the transference data, 

 and that they would thus establish the fact that a marked change in the 

 relative migration-velocity of the ions of acids takes place on passing 

 to very low concentrations. Nitric acid was selected as the second acid, 

 since it is of quite a different chemical character.* Another purpose of 

 this investigation, bearing directly on the third suggestion mentioned 

 above, was to extend the transference measurements with both acids to 

 a dilution of about 0.002 normal. 



112. PREPARATION AND STANDARDIZATION OF THE SOLUTIONS. 



The chemically pure nitric acid of trade was freed from lower oxides 

 of nitrogen by diluting it with two-thirds its volume of conductivity 

 water and drawing a current of purified air through it. It was care- 

 fully tested (using 5-10 c.cm.) for chloride with silver nitrate, for sul- 

 phate by evaporation with barium chloride, for ammonia with Nessler 

 reagent, and for nitrite by diluting and adding starch and potassium 

 iodide. These impurities could not be detected at all, or were present 

 only in entirely insignificant quantity. Diluter solutions (from 0.06 to 

 0.0006 normal) were made up with water having in all cases a specific con- 

 ductance lying between 0.9 and 1.2 X 10" 6 reciprocal ohms at 18, and 

 were titrated with the help of phenolphthalein against a 0.1 normal solu- 

 tion of barium hydroxide, which had been repeatedly crystallized and 

 was proved to be substantially free from chloride, and also from silica, 

 calcium, strontium, or other metals than barium (by precipitating with 

 sulphuric acid and evaporating the filtrate to dryness in a platinum dish, 

 when a scarcely weighable residue was obtained). The strength of the 

 barium hydroxide solution was determined gravimetrically both by pre- 

 cipitating with sulphuric acid after neutralizing with hydrochloric acid 

 and by evaporating to dryness with pure nitric acid and weighing the resi- 

 due of Ba(N0 3 ) 2 after heating to 160 - 180. The two methods gave for 



the content of the solution in milli-equivalents per kilogram jno!58[ 

 and {HJJ'Zff respectively; the value adopted was 110.64. Afterwards 



two other solutions of barium hydroxide were prepared and titrated 

 against nitric acid solutions which had been standardized against the first 

 barium hydroxide solution. Solution No. 2 contained 0.11904,f and solu- 

 tion No. 3 contained 0.05859$ equivalents per kilogram of solution. 



The five solutions of nitric acid varying from about 0.06 to 0.006 



*A single transference experiment has already been made with this acid at 25 

 at 0.05 normal concentration by Bein (Z. phys. Chem., 27, 44. 1898). 



fl86.83 gm. of this solution (the total amount used in three concordant experi- 

 ments) neutralized 388.08 gms. of HNOs Sol. No. 2. 



$118.19 gm. of this solution (used in five concordant experiments) neutralized 

 1048.90 gms. of HN0 3 Sol. No. 5. 



